In order to generate clock signals in information equipments, a piezoelectric oscillator is widely used, in which a piezoelectric material such as a crystal or barium titanate is used. The piezoelectric oscillator includes a substrate made of the piezoelectric material having a predetermined length and thickness, excitation electrode patterns formed on both surfaces of the substrate, and leading lines that extend from the electrode patterns. The substrate functions as a piezoelectric vibrator. One part of the substrate is mechanically fixed inside a package, and another part of the substrate is oscillated mechanically.
One of known methods for mechanically supporting the piezoelectric vibrator is a cantilever method, in which one end of the piezoelectric vibrator is not mechanically fixed so as to be a free end.
FIG. 4A illustrates a plan view of a piezoelectric oscillator 10, without a lid, including a piezoelectric vibrator 20 in a cantilever fashion. FIG. 4B illustrates a lateral view of the piezoelectric oscillator 10, with a lid 40, cut along a line A-A′ in FIG. 4A. The piezoelectric vibrator 20 of the piezoelectric oscillator 10 is provided inside a package 30. The piezoelectric vibrator 20 is a substrate made of a crystal or the like. An electrode pattern 21 and a leading line pattern 22 that extends from the electrode pattern 21 are formed on the upper surface of the piezoelectric vibrator 20 by a thin film formation technique such as a metallic vapor deposition technique. Similarly, a lower surface electrode pattern (not illustrated) and a leading line pattern 24 that extends from the lower surface electrode pattern are formed on the lower surface of the piezoelectric vibrator 20. The package 30 is made of a material such as ceramic and has a step 31 formed therein. Metal pads 32 and 34 are formed on the step 31 by metalization. Conductive adhesives 33 and 35 are respectively applied to the metal pads 32 and 34. Then, in this state, ends of the leading line patterns 22 and 24 formed on the piezoelectric vibrator 20 are respectively placed on the conductive adhesives 33 and 35, and then the conductive adhesives 33 and 35 are cured. The curing of the conductive adhesives 33 and 35 allows the piezoelectric vibrator 20 to be supported on the step 31 substantially horizontally in a cantilever fashion.
Each of the metal pads 32 and 34 formed on the step 31 is connected to an external electrode (not illustrated), which is formed on the bottom of the package 30 by metallization, through a conductor (not illustrated) provided inside the package 30. The external electrode applies a voltage to the piezoelectric oscillator 10 provided on a circuit substrate. The piezoelectric vibrator 20 is deformed by a voltage effect and is therefore oscillated at a resonant frequency, thereby obtaining a voltage signal corresponding to the frequency.
In this example, only the piezoelectric vibrator is accommodated in the package, but a semiconductor device of an oscillation circuit may be accommodated in the package along with the piezoelectric vibrator. FIG. 5 illustrates a lateral view of a piezoelectric oscillator 11 accommodated with a semiconductor device 50 therein. This configuration allows a packaging density on the circuit substrate to be improved. Because the semiconductor device 50 in addition to the piezoelectric vibrator 20 is accommodated in the package 30, the free space inside the package 30 becomes smaller. Therefore, control for keeping the piezoelectric vibrator 20 not to contact a lid 40 and the semiconductor device 50 becomes more difficult.
A ceramic package made of alumina (Al2O3) is typically used as the package of the piezoelectric oscillator.
The package made of alumina is nontransparent, however, a transparent package made of a hard glass material is also known. Japanese Laid-open Patent Publication No. 2008-42512 discloses a related technique.
A known method for forming a cantilever piezoelectric vibrator includes the following processes: placing a free end of the piezoelectric vibrator on a temporary supporting member (pillow member), which is positioned on a floor surface inside the package, made of a resin having a heat shrinkage property or a thermal deformation property; placing a supported end of the piezoelectric vibrator on the conductive adhesives applied to the step of the package; curing the conductive adhesives; and deforming the temporary supporting member by heating to form a gap between the piezoelectric vibrator and the temporary supporting member. The temporary supporting member is separated from the piezoelectric vibrator after the fixation of the supported end, thereby allowing the piezoelectric vibrator to be supported substantially horizontally in a cantilever fashion. Accordingly, contact of the free end with the package is suppressed. Japanese Laid-open Patent Publication No. 2006-80599 and Japanese Patent No. 4214753 disclose relates techniques.
One end of the cantilever piezoelectric vibrator is free, and this allows the piezoelectric vibrator not to be mechanically restrained. Therefore, the cantilever piezoelectric vibrator is widely used because the supported portion is less affected by stress due to vibration. However, recently, the size of electronic devices has been decreasing, and electronic components have been required to have a low height. Accordingly, available space in the package to place the piezoelectric vibrator is reduced. In cases where the piezoelectric vibrator is fixed while being tilted, the piezoelectric vibrator may contact the package. Therefore, the piezoelectric vibrator is required to be more accurately supported horizontally in a cantilever fashion. Also in cases where the semiconductor device of the oscillation circuit is accommodated in the package along with the piezoelectric vibrator, the same requirement arises as in the case in which electronic components are required to have a low height.